1. Field of the Invention
The present invention relates to a control system for an internal combustion engine, and particularly to a control system for an internal combustion engine provided with an exhaust gas recirculation mechanism for recirculating exhaust gases to an intake passage.
2. Description of Related Art
A method is conventionally known for opening and closing an exhaust gas recirculation valve in a fuel-cut operation of an internal combustion engine, where the supply of fuel to the engine is interrupted, and for determining abnormality of an exhaust gas recirculation mechanism according to a change in intake pressure, i.e., a decrease in exhaust gas recirculation amount due to clogging of an exhaust gas recirculation passage or the exhaust gas recirculation valve (Japanese Patent Laid-open No. Hei 7-180615).
In executing abnormality determination for the exhaust gas recirculation mechanism by using the above method, the exhaust gas recirculation valve is opened and closed in the fuel-cut operation of the engine, so that the exhaust gas recirculation passage is filled with air rather than exhaust gases. Accordingly, when the exhaust gas recirculation valve is then opened in the above condition, the air present in the exhaust gas recirculation passage is first supplied to the intake passage, and exhaust gases are thereafter supplied to the intake passage. As a result, if a fuel amount based on the assumption that exhaust gases are recirculated simultaneously with opening of the exhaust gas recirculation valve is supplied to the engine, there is a problem that the fuel amount becomes insufficient and the air-fuel ratio becomes leaner than a desired value. Further, an ignition timing of the engine is set to different values between when executing exhaust gas recirculation and when not executing exhaust gas recirculation, so that the ignition timing immediately after opening the exhaust gas recirculation valve deviates from an optimum ignition timing.
It is accordingly an object of the present invention to provide a control system for an internal combustion engine which can more properly set an engine control amount immediately after opening an exhaust gas recirculation valve after finishing the abnormality determination of an exhaust gas recirculation mechanism.
In accordance with the present invention, provided is a control system for controlling an internal combustion engine having an exhaust passage and an intake passage. The control system comprises an exhaust gas recirculation mechanism, a control means, a fuel supply interrupting means, a pressure detecting means, a pressure change calculating means, and abnormality determining means. The exhaust gas recirculation mechanism includes an exhaust gas recirculation passage connected between the exhaust passage and the intake passage, and an exhaust gas recirculation valve provided in the exhaust gas recirculation passage for controlling an exhaust gas amount to be recirculated from the exhaust passage through the exhaust gas recirculation passage to the intake passage. The control means is for calculating at least one control parameter of the engine according to operating conditions of the engine including an open/closed condition of the exhaust gas recirculation valve and controlling the engine by using the calculated at least one control parameter. The fuel supply interrupting means is for interrupting the supply of fuel to the engine in a decelerating operation of the engine. The pressure detecting means is for detecting an intake pressure in the intake passage. The pressure change calculating means is for calculating an amount of change in the intake pressure between when opening the exhaust gas recirculation valve and when closing the exhaust gas recirculation valve, in a fuel-cut operation where the fuel supply to the engine is interrupted by the fuel supply interrupting means. The abnormality determining means is for determining the abnormality of the exhaust gas recirculation mechanism according to the amount of change in the intake pressure. The control means controls the engine by using the at least one control parameter suitable for a closed condition of the exhaust gas recirculation valve during a predetermined time period from the time of first opening of the exhaust gas recirculation valve after finishing the abnormality determination by the abnormality determining means.
With this configuration, when first opening the exhaust gas recirculation valve after finishing the abnormality determination by the abnormality determining means, one or more control parameters suitable for the closed condition of the exhaust gas recirculation valve is/are used during the predetermined time period from the time of opening the exhaust gas recirculation valve. Accordingly, the control parameter(s) of the engine can be set to a more proper value corresponding to the supply of the air in the exhaust gas recirculation passage to the intake passage immediately after opening the exhaust gas recirculation valve after finishing the abnormality determination for the exhaust gas recirculation mechanism. As a result, a deterioration in exhaust emission characteristics and output characteristics of the engine can be prevented, and good operating characteristics of the engine can be maintained.
Preferably, the predetermined time period is a time period required for almost all quantity of air filling the exhaust gas recirculation passage to flow into the intake passage.
Preferably, the control system further comprises a lift sensor for detecting an actual valve lift amount of the exhaust gas recirculation valve. The control means accumulates the actual valve lift amount detected by the lift sensor from the time of first opening of the exhaust gas recirculation valve after finishing the abnormality determination by the abnormality determining means to thereby calculate the accumulated value of actual valve lift amounts, and the predetermined time period is set to a time period until the accumulated value of actual valve lift amounts reaches a predetermined value.
Alternatively, the predetermined time period may be a fixed time period.
Preferably, the pressure change calculating means includes reliability determining means for determining reliability of the calculated amount change in the intake pressure; and the pressure change calculating means calculates a change in the intake pressure again, when the reliability determining means determines that the reliability of the calculated amount of change in the intake pressure is low.
Preferably, the control parameter(s) include at least one of a fuel amount to be supplied to the engine and an ignition timing of the engine.
Preferably, the pressure change calculating means corrects the amount of change in the intake pressure detected by the pressure detecting means according to a rotational speed of the engine to thereby calculate the amount of change in the intake pressure.
Preferably, the control system further comprises deterioration parameter calculating means for calculating a deterioration parameter indicative of a degree of deterioration of the exhaust gas recirculation mechanism, according to the amount of change in the intake pressure between when opening the exhaust gas recirculation valve and when closing the exhaust gas recirculation valve in the fuel-cut operation. The control means corrects the at least one control parameter according to the deterioration parameter when the exhaust gas recirculation valve is open.